burns



March 17, 1964 w. E. BURNS SOUND GENERATING DEVICE FOR CODE PRACTICE Filed Feb. 2. 1961 m 1 R U B E VM 6 NA w W L 0 B ATTORNEY United States Patent 3,125,752 SOUND GENERATING DEVICE FOR CQDE PRACTICE William E. Burns, 123 Dolly Lane, Chalfont, Pa. Filed Feb. 2, 1961, Ser. No. 86,717 1 Claim. (Cl. 340-388) This invention relates to acoustical devices and more particularly to a sound generating device for code practice.

A general object of the invention is an inexpensive acoustical element suitable for use in an educational device to reproduce the sound of a high frequency radio signal.

One object of the invention is a compact and sturdy electroacoustical device adapted to simulate a variety of high frequency radio signals.

Another object is an electroacoustical device employing a metallic member and so arranged and constructed to vibrate at the actual frequency of the member.

Another object is an electroacoustical device employing a metallic member as a vibrating element and including means to reinforce the sound of the vibrating element to reproduce a wide variety of high frequency sounds emanating from a radio transmitter.

Still another object is an acoustical device adapted to produce a variety of pleasing sounds for use in a musical toy or the like.

These and other objects are accomplished in the present invention, one illustrative embodiment of which comprises a cup shaped non-metallic base member including means for mounting an electrical coil of a preselected number of turns. The base member also includes means for mounting a metallic diaphragm of preselected thickness so as to be within the field of the magnetic coil. A first contact is positioned on the diaphragm so as to be adjacent an edge thereof. An adjustable arm member is secured to the base and includes a second contact which cooperates with the first contact. Completing the device is a cover which slides over the base to trap the air above the diaphragm so that when the coil is energized, the diaphragm alternately opens and closes the first and second contacts to generate a vibrating sound from the diaphragm which is reinforced by the trapped air held within the enclosure.

In the drawing:

FIG. 1 is an exploded View of the various elements included in one illustrative embodiment of the present invention;

FIG. 2 is a side view, partially cut away, of the elements of FIG. 1 in assembled relation;

FIG. 3 is a top view of the elements included in FIG. 1 in an assembled position; and

FIG. 4 is an electrical schematic of the embodiment shown in FIG. 1.

Referring to FIGS. 1, 2 and 3, one illustrative embodiment includes a base member 20 which may be of any non-metallic material, typically plastic or rubber, which has the quality of absorbing sound. The base member is cup shaped and includes a shoulder portion 22 for reasons more apparent hereinafter. Also, included in the base member is a slot 24 along the longitudinal axis of the base. A central aperture 26 includes a fastener 28 to which is attached a bobbin 30 the latter supporting a coil 32 of wire which is adapted to be intermittently energized from a source of electrical power. The fastener 26 prevents relative movement of the coil and bobbin with respect to the base member.

In order to connect the coil 32 to a supply of current 34 (see FIG. 4) terminals 36 and 38 are suitably mounted in the base member. The terminal 36 is connected to "ice one side of the coil and the terminal 38 is connected to the other side of the coil. The terminal 38 is also connected to a contact 42 secured to a disc member 48, typically metal.

The disc member 40 is positioned on the shoulders 22 in order to vibrate in an unrestrained manner. The natural frequency of the disc member 40 can be determined from the thickness, radius, modulus of elasticity, density of material and other factors in accordance with wellknown formulae. The natural frequency of the disc is selected to correspond to that of a high frequency radio signal, which is of the order of several hundreds (900) of cycles per second. It should be apparent that changing the thickness and the diameter of the disc will produce natural frequencies of different magnitudes.

The position of the disc member with respect to the bottom of the base member is selected to be of a distance that the trapped air within the base will generate standing waves when vibrations of the disc occur, the standing waves improving the pitch of the sound generated by the vibrating disc. The disc is limited in movement along the vertical axis of the base by an O ring 43 of rubber or like material, the ring being snapped into position above the disc and along the wall of the shoulder 22. Movement of the disc in a direction normal to the (vertical) axis of the base is prevented by making the diameter of the disc approximate that of the base at the shoulder 22. A clearance of five to ten thousandths of an inch exists between the sides of the shoulder and the disc to provide the disc with freedom of movement.

The disc contact 42 normally mates with a contact 44 which is secured to an adjustable cantilever member 46. Fasteners 48 secure the cantilever member to the exterior of the base member 20 and also permit connection of a return line 49 to the supply 34. The cantilever member also includes a tapped opening 59 at the unsecured end thereof which receives a bolt 52 which extends through the slot 24 of the base member. Rotation of the bolt member 52 adjusts the tightness of the mating contacts 42 and 44, which in turn affects the amplitude of disc vibration, as will be described in more detail hereinafter.

Completing the assembly of the acoustical element is a cover 54 having a series of openings 56 therein. The cover is adapted to receive the base member so that the combination appears as a single unit which may be easily separated for cleaning and repair of the acoustical parts. The openings 56 permit air to be partially trapped above the disc whereby the partially trapped air will also improve the quality of the pitch developed when the disc member vibrates. The effect of the partially trapped air is to add to the volume and quality of the sound similar to the effect of a horn on a mouth piece. A slip ring 60 having apertures 62 thereon cooperates with the openings 56 to change the pitch of the sound generating from the vibrating diaphragm, the slip ring varying the amount of confinement of the air.

Turning to FIG. 4, the electrical circuit is shown for creating a magnetic field which applies a periodic force to the disc to cause vibrations thereof. The supply 34 is connected across the coil 32 through connection to the terminals 36 and 48. The supply provides sufficient current to the coil such that a magnetic field is established that will attract the disc toward the coil. A switch 55 when operated, completes the electrical circuit between the supply 34 and the coil 32. It should be recalled of course, that the contacts 42 and 44 are normally closed when the switch is open and on closure of the switch 55, the magnetic field developed by the coil 32 attracts the disc 40 toward the coil 32. As a consequence, the contacts 42 and 44 will separate and open the electrical circuit. The stifi'ness of the disc will thereupon restore the contacts 42 and 44 to the normally mating or closed condition to recomplete the electrical circuit and again attract the disc toward the coil. This process is repeated so long as the switch 55 is closed.

To obtain a vibrating frequency of the disc which most realistically approximates the sound of high frequency radio equipment, it has been found that the contacts 42 and 44 must be eccentrically located with respect to the center of the disc 40. Experiment has confirmed that contacts located near the periphery of the disc will produce the sound most like that of operating radio equipment.

The volume of the vibrating sound is controlled by adjusting the cantilever member 46 with the bolt 52. When the bolt 52 is rotated clockwise, the cantilever 46 is pulled down and the contacts 42 and 44 are urged into tighter contact. As a consequence, the amplitude of the vibrating disc will be increased due to the greater deflection needed to break contacts and'the volume of the sound will be greater. Conversely, when the bolt 52 is rotated counter-clockwise, the cantilever 46 will be raised and the pressure of the mating contacts 42 and 44 reduced. The amplitude of the vibrating disc will be lowered and the volume of the sound from the vibrating disc will decrease. Thus a simple and reliable means are provided to adjust the volume of sound emanating from the vibrating disc.

What is claimed is:

A sound generating device for code practice adapted to produce a variety of sound signals comprising a cup shaped base member of non-metallic material, an electro- 4 magnet suitably mounted Within the cup shaped member, a disc member having a natural frequency of the order of several hundreds of cycles per second, said disc member being positioned adjacent'to the said magnet, means for limiting longitudinal movement of the disc member with respect to the base member, said disc member including a contact which is electrically connected to the electromagnet, a cantilever member including a contact which normally mates with the contact of the disc member, said cantilever member also including a tapped hole at the unsecured'end thereof, a bolt member which engages the tapped hole of the cantilever member" to adjust the pressure of the mating cantilever and disc contact, means for connecting a supply of current through the electromagnet and the mating cantilever and disc contacts so that the disc is attracted toward the electromagnet and returned to engagement with the cantilever contact to produce a pitch which-approximates the frequency of the disc member, and a cover member which encloses the base member and controllablytraps air above the disc member to improve the quality and vary the frequency of the pitch generated by the vibrating disc member.

References Cited in the file of this patent UNITED STATES PATENTS 1,994,426 Billig Mar. 12, 1935 2,645,768 Santino July 14, 1953 2,977,418 Haas Mar. 28, 1961 2,994,078 Uchihara July 25, 1961 

